This invention relates to a sheet metal working tool and more particularly to a method and apparatus for pulling out dents from automobile sheet metal bodies.
In the art of automotive body repairing where access is readily available to only one side of the damaged sheet metal it is difficult with conventional tools to pull out an indentation. The mechanic, in such cases where a mallet and a hand-held anvil cannot be utilized, must use a tool that pulls from the blind side. Conventionally the tool comprises a screw member at one end of a rod having a gripping handle at the other end with a slide hammer in between. A number of holes are drilled into the dented area of the sheet metal body and the screw member is threaded in turn into each of the holes and the hammer is forcibly moved along the rod into engagement with a stop adjacent the handle. The process is repeated for each hole until the dented area conforms to the overall contour of the body, at which time the holes are sealed with body putty.
One difficulty with tools of the aforementioned type is that the area around each hole is upset and jaggered sheet metal projects outwardly about the periphery of each hole thereby requiring excessive grinding. Another difficulty is that excessive pulling may stretch the body locally resulting in mechanical weakness or even cracks extending through the dented area which must be carefully ground and filled.
It is also known in the prior art to use dent pullers having a hook at the free end for insertion within pre-drilled holes so as to eliminate upsetting of the metal about the hole. Tools of this character are illustrated in U.S. Pat. Nos. 2,900,853 and 3,100,336. In U.S. Pat. No. 3,222,915 a hollow expandable tip is inserted into a hole in the dent and the tip expands when a pulling force is exerted on a rod having a flared end and disposed concentrically within the tip, and which operates similar to tube expanders of the type illustrated in U.S. Pat. No. 3,236,104. In U.S. Pat. No. 3,765,220 a dent puller in the form of a fork-member is used in conjunction with anchor members secured at a number of locations within the dent, the anchors being pulled by the fork-member.
In each of the known prior art devices difficulties are encountered when dents, and especially large dents, are to be repaired. In the hook type tools the pulling force is concentrated on one side and thus tends to result in pivoting of the hook such that the end thereof excessively strains the metal against which it engages. In the known expanding type pullers the expansion is limited and thus they act to pull a limited area. This is also true of the anchor and hook type puller which, since it requires securement of the anchors to the dent, evolves a time consuming process.